Migration to cloud from on premise

We have a requirement to migrate the application from on premise to cloud. Could anyone help me with steps to follow for cloud migration.

The main challenge for us is, we have set of documents uploaded by users through UI, IDs of those documents are stored in DB and documents are stored in one of the folder of Knowledge Center. So what will be best approach to move all the documents to cloud ? After moving to cloud there should not be any folder ID or Document ID conflicts because again end users of the application will be downloading the documents from UI. 

Please for better approach.

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